Commissioning is the final stage before an electrical installation is put into service. It covers initial verification testing, functional checks of every device, snagging, documentation, and formal handover to the client. This guide explains the complete process for domestic and commercial installations.
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Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.
Commissioning is the final stage before an installation is put into service. It combines initial verification (inspection and testing to BS 7671 Chapter 64), functional testing of every device under Regulation 643.10, snagging of minor defects, completion of all documentation, and formal handover. Testing confirms each circuit; commissioning confirms the whole installation works and is ready for the client to use.
On a simple domestic job the distinction is small — verification effectively is the commissioning. On commercial and industrial projects commissioning is a separate, programmed phase with its own records and sign-off.
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Commissioning is the process of bringing an electrical installation from completion of physical installation through to handover as a fully tested, documented, and operational system. It is the final stage before the installation is put into service and the client takes ownership.
Commissioning includes initial verification (inspection and testing to BS 7671 Chapter 64), functional checks of all equipment and controls, snagging and rectification of minor defects, completion of all documentation (certificates, drawings, manuals), and formal handover to the client.
For a simple domestic job — such as a consumer unit replacement or a new circuit installation — commissioning is straightforward: test the installation, confirm everything works, issue the EIC, and hand it to the client. For a large commercial or industrial project, commissioning is a structured phase of the project with its own programme, team, and sign-off procedures.
Regardless of the scale, the principle is the same: do not hand over an installation until you have confirmed it works correctly, documented the evidence, and given the client everything they need to use and maintain it safely.
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Testing (initial verification) confirms that individual circuits meet BS 7671 requirements — continuity, insulation resistance, earth fault loop impedance, RCD operation, and so on. Commissioning confirms that the installation works as a complete system.
Testing answers the question: "Does each circuit meet BS 7671?" Commissioning answers the broader question: "Does the entire installation work as intended and is it ready for the client to use?"
Commissioning time scales with the complexity of the installation, not just its size. The instrument testing of initial verification is usually the largest single block of time, but functional checks, snagging and documentation all add to it. These are indicative planning figures, not a quote — always build commissioning into the project programme from the start rather than squeezing it into the final day.
For domestic work the documentation can be completed on site as you test — see the testing sequence guide for the order the tests are carried out. On larger projects the commissioning phase is planned, resourced and signed off in its own right.
Functional checks go beyond the instrument-based testing of initial verification. They involve physically operating every device in the installation to confirm it works correctly. BS 7671 Regulation 643.10 requires equipment — including switchgear and controlgear assemblies, drives, controls and interlocks — to be functionally tested as appropriate, to verify it is properly mounted, adjusted and installed and operates correctly.
Record the results of all functional checks. For domestic work, this is typically noted on the EIC. For commercial projects, a separate commissioning record sheet is used.
Proper documentation is a core part of commissioning. The documentation package serves as evidence that the installation has been tested and is fit for purpose. It is also the reference that future electricians will use when maintaining or modifying the installation. For the full breakdown of what belongs in the pack, see the handover documentation guide.
What actually needs handing over depends on the job. A consumer unit change needs the core certificate package; a commercial fit-out adds a full deliverables file. This matrix shows the typical split:
For Part P notifiable work, the EIC must be registered with building control (either directly or through a competent person scheme). Failure to certify notifiable work is a building regulation offence.
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Handover is the formal point at which the client takes responsibility for the installation. A good handover ensures the client understands what has been installed, how to use it safely, and what documentation they should keep.
For commercial projects, handover may involve a formal meeting with the client's facilities management team, structured training on specialist equipment, and a sign-off document confirming the client has received all documentation and is satisfied with the installation.
Finished commissioning? Export the EIC as a professional PDF and send it to the client by email or WhatsApp — before you leave site.
Try it free for 7 daysOperation and Maintenance (O&M) manuals are detailed documents that describe how to operate and maintain the installed equipment. They are standard practice on commercial and industrial projects, and increasingly expected on larger domestic installations.
For domestic work, a formal O&M manual is not usually required — the EIC, circuit chart, and manufacturer instructions are sufficient. For commercial projects, the O&M manual is a contractual deliverable and must be provided before practical completion is certified under the building contract.
Use this checklist to ensure nothing is missed during commissioning. Tick off each item as it is completed:
Pro tip: Take photographs of the completed installation — the consumer unit (cover on and off), cable routing, earthing and bonding connections, and any concealed wiring before it is covered. These photos are invaluable for future maintenance and can be attached to the EIC in Elec-Mate.
Elec-Mate handles the certification and documentation side of commissioning so you can focus on the testing and functional checks. Here is how it fits into your commissioning workflow:
Photograph the new consumer unit. The AI reads MCB/RCBO ratings and circuit labels from the image. The EIC schedule pre-fills with circuit descriptions and protective device details.
Speak your test results as you work through the test sequence. Dead test results and live test results populate the schedule automatically. AI compares every value against BS 7671 limits.
The completed EIC exports as a professional PDF. Send it to the client by email or WhatsApp from site. Attach the invoice. The client has the commissioning documentation before you leave the property.
AI board scanner, voice test entry, automatic BS 7671 compliance checking, and instant PDF export. Complete the EIC on site and hand it over digitally.
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